Thermal relief mechanism for combination-type heat exchangers

ABSTRACT

A multi-fluid heat exchanger ( 10 ) is provided for transferring heat between a common fluid and a first fluid in one core section ( 22 ), and between the common fluid and a second fluid in another core section ( 28 ) of the heat exchanger ( 10 ). The core sections ( 22,28 ) are located in a series arrangement with respect to the flow of the common fluid through the heat exchanger ( 10 ) by folding the heat exchanger ( 10 ), with the core sections ( 22,28 ) being connected by folded portions ( 20 ) of the header pipes ( 12,14 ) that direct the first and second fluid flows to the interiors of the core sections ( 22,28 ).

FIELD OF THE INVENTION

This invention relates to heat exchangers and more particularly tocombination-type heat exchangers wherein heat exchanger cores for two ormore fluids share a common manifold or header, and in more particularapplications, to such heat exchangers as used in vehicular systems, suchas automobiles, buses, trucks, etc.

BACKGROUND OF THE INVENTION

It is known to form a so-called “combination” or “combo” type heatexchanger by including one or more baffles in each of the manifolds orheaders of the heat exchanger to divide the interiors of each of theheaders into at least a first section for a first working fluid and asecond section for a second working fluid, with each of the workingfluids being directed through the respective heat exchange tubes thatare connected to the respective sections of the common manifolds. Theresulting structure provides a “stacked” arrangement of heat exchangercores. While such constructions may be suitable for their intendedpurposes, problems can arise when there are space limitations and one orboth of the combined heat exchangers requires more capacity (i.e., moreface area). Accordingly, there is a continued need for improvement incombo heat exchangers.

SUMMARY OF THE INVENTION

In accordance with one feature of the invention a multi-fluid heatexchanger is provided for transferring heat between a common fluid and afirst fluid in one part of the heat exchanger and between the commonfluid and a second fluid in another part of the heat exchanger. The heatexchanger includes a pair of spaced, elongated header pipes to directthe first and second fluids to and from the heat exchanger, each of theheader pipes including a first fluid manifold for the first fluid and asecond fluid manifold for the second fluid with the first and secondfluid manifolds connected by a folded portion of the elongate headerpipe. The heat exchanger further includes a first core section totransfer heat between the common fluid and the first fluid as the commonand first fluids pass through the first core section, the first coresection extending between the header pipes and connected at oppositesides to the first fluid manifold in each header to transfer the firstfluid between the header pipes and the first core section, and a secondcore section to transfer heat between the common fluid and the secondfluid as the common and second fluids pass through the second coresection, the second core section extending between the header pipes andconnected at opposite sides to the second fluid manifold in each headerto transfer the second fluid between the header pipes and the secondcore section. The second core section is positioned downstream from thefirst core section with respect to a flow direction of the common fluidthrough the first and second core sections to receive the common fluidafter it has passed through the first core section.

In one feature, the multi-fluid heat exchanger further includes astructural support on one of the header pipes and connected to both thefirst and second fluid manifolds at a location spaced from the foldedportion.

According to one feature, the first and second manifolds of each headerpipe are separated from each other by a cut located adjacent the foldedportion.

As one feature, each of the header pipes is a cylindrical tube having aplurality of tube receiving openings spaced along a length of the headerpipe to receive ends of heat exchange tubes from the first and secondcores.

In one feature, each of the first and second cores includes a pluralityof parallel, spaced, flattened tubes, each of the tubes having a firstend and a second end, with the first end received in one of the headerpipes and the second end received in the other header pipe to direct thecorresponding one of the first and second fluids between the first andsecond header pipes through an interior of the tube. In a furtherfeature, each of the first and second cores further includes corrugatedfins extending between adjacent pairs of said tubes.

In accordance with one feature of the invention, a multi-fluid heatexchanger is provided for transferring heat between a first fluid and acommon fluid in one part of the heat exchanger and between a secondfluid and the common fluid in a second part of the heat exchanger. Theheat exchanger includes a first core section, a second core section, anda first elongated header pipe having a plurality tube receiving openingsspaced along a length of the first header pipe, a second elongate headerpipe having a plurality of tube receiving openings spaced along a lengthof the second header pipe. The first core section includes a pluralityof parallel, spaced tubes, each of the tubes having a first end and asecond end, with the first end received in a corresponding one of thetube receiving openings of the first header pipe and the second endreceived in a corresponding one of the tube receiving openings of thesecond header pipe to direct the first fluid between the first andsecond header pipes through an interior of the tube. The second coresection includes a plurality of parallel, spaced tubes, each of thetubes having a first end and a second end, with the first end receivedin a corresponding one of the tube receiving openings of the firstheader pipe and the second end received in a corresponding one of thetube receiving openings of the second header pipe to direct the secondfluid between the first and second header pipes through an interior ofthe tube. Each of the header pipes has a folded portion at a locationbetween the first and second cores to locate the second core downstreamfrom the first core with respect to a flow path of the common fluidthrough the first and second cores.

As one feature, each of the header pipes includes a cut adjacent thefolded portion between the first and second manifolds.

In one feature, each of the header pipes includes a cylindrical tubehaving the tube receiving holes formed therein.

According to one feature, the tubes of at least one of the cores areflattened tubes and the at least one of the cores further comprisescorrugated fins extending between each adjacent pair of flattened tubes.

As one feature, the multi-fluid heat exchanger further includes astructural support on one of the header pipes and connected to both thefirst and second fluid manifolds at a location spaced from the foldedportion.

In one feature, the multi-fluid heat exchanger further includes a thirdcore section to transfer heat between the common fluid and a third fluidas the common and third fluids pass through the third core section. Thethird core section extends between the header pipes and is connected atopposite sides to a third fluid manifold in each header to transfer thethird fluid between the header pipes and the third core section. Thethird fluid manifold is connected to one of the first and second fluidmanifolds by another folded portion of the elongate header pipe. Thethird core section is positioned relative to at least one of the firstand second core sections so that the common fluid passes through thethird core section and the at least one of the first and second coresections in series fashion.

In accordance with one feature of the invention, a method is providedfor making a multi-fluid heat exchanger for transferring heat between afirst fluid and a common fluid in one part of the heat exchanger andbetween a second fluid and the common fluid in a second part of the heatexchanger. The method includes the steps of:

a) providing a heat exchanger with first and second core sectionsextending between a pair of elongated header pipes, with each of theheader pipes having a first fluid manifold for the first core sectionand a second fluid manifold for the second core section;

b) providing a cut portion in each of the header pipes at a locationbetween the first and second fluid manifolds, the cut portion leaving atleast part of the header pipe connecting the first and second fluidmanifolds of the header; and

c) folding the heat exchanger at the cut portion so that the at leastpart of the header pipe is deformed and the first and second coreportions are located in series with respect to a flow path for thecommon fluid through the first and second core portions.

In one feature, the method further includes the step of connecting thefirst and second manifolds of at least one of the header pipes to eachother at a location spaced from the cut portion after step c).

According to one feature, the method further includes the step ofbrazing the first and second core sections and the pair of elongatedheader pipes as an assembly prior to step c).

As one feature, the method further includes the step of brazing thefirst and second core sections and the pair of elongated header pipes asan assembly prior to step b).

In one feature, the method further includes the steps of:

d) providing the heat exchanger with a third core section extendingbetween the pair of elongate header pipes, with each of the header pipeshaving a third fluid manifold for the third core section;

e) providing an additional cut portion in each of the header pipes at alocation between the third fluid manifold and one of the first andsecond fluid manifolds, the additional cut portion leaving at least partof the header pipe connecting the third fluid manifold and the one ofthe first and second fluid manifolds of the header; and

f) folding the heat exchanger at the additional cut portion so that theat least part of the header pipe connecting the third fluid manifold andthe one of the first and second fluid manifolds is deformed and thethird core section is located in series with at least one of the firstand second core sections with respect to a flow path for the commonfluid through the third core section and the at least one of the firstand second core sections.

In accordance with one feature of the invention, a method is providedfor making a pair of heat exchangers for transferring heat between afirst fluid and a common fluid in one of the heat exchangers and betweena second fluid and the common fluid in the other of the heat exchangers.The method includes the steps of:

a) providing a heat exchanger with first and second core sectionsextending between a pair of elongated header pipes, with each of thepipes having a first fluid manifold for the first core section and asecond fluid manifold for the second core section; and

b) completely severing each of the header pipes at a location betweenthe first and second fluid manifolds to form the pair of heatexchangers, with one heat exchanger including the first fluid manifoldsand the first core section, and the other heat exchanger including thesecond fluid manifolds and the second core section.

In one feature, the method further includes the step of securing thepair of heat exchangers to each other so that the first and second coreportions are located in series with respect to a flow path for thecommon fluid through the pair of heat exchangers after step b).

Other advantages, features, and objects of the invention will berealized by a detailed review of the entire specification, including theappended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are somewhat diagrammatic front elevations of amulti-fluid heat exchanger embodying the present invention, with FIG. 1Ashowing the heat exchanger before it is has been folded, and FIG. 1Bshowing the heat exchanger in its final, folded form;

FIGS. 2A and 2B are enlarged diagrammatic representations taken fromline 2-2 in FIGS. 1A and 1B;

FIG. 3 is a view taken from line 3-3 in FIG. 1A showing more details ofone preferred form of the heat exchanger of FIGS. 1A-2B;

FIG. 4 is a view similar to FIG. 2B but illustrating another embodimentof the invention; and

FIGS. 5 and 6 are views similar to FIG. 2A showing alternate embodimentsof a multi-fluid heat exchanger embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1A-2B, a multi-fluid heat exchanger 10 is shownfor transferring heat between a common fluid (shown schematically byarrows A in FIG. 2B) and a first fluid (shown schematically by arrows Bin FIGS. 1A and 1B) in one part of the heat exchanger and between thecommon fluid and a second fluid (shown schematically by arrows C inFIGS. 1A and 1B) in another part of the heat exchanger 10. The heatexchanger 10 includes a pair of spaced, elongated header pipes 12 and 14to direct the first and second fluids to and from the heat exchanger.Each of the header pipes 12,14 includes a first fluid manifold 16 forthe first fluid and a second fluid manifold 18 for the second fluid,with the first and second fluid manifolds 16 and 18 being connected by afolded portion 20 of the elongate header pipe, best seen in FIG. 2B. Theheat exchanger 10 further includes a first core section 22 to transferheat between the common fluid and the first fluid as the common andfirst fluids pass through the first core section 22. The first coresection 22 extends between the header pipes 12,14 and is connected atopposite sides 24 and 26 to the first fluid manifold 16 in each headerpipe 12,14 to transfer the first fluid between the header pipes 12,14and the first core section 22. The heat exchanger also includes a secondcore section 28 to transfer heat between the common fluid and the secondfluid as the common and second fluids pass through the second coresection 28. The second core section 28 extends between the header pipes12,14 and is connected at the opposite sides 24 and 26 to the secondfluid manifold 18 in each header pipe 12,14 to transfer the second fluidbetween the header pipes 12 and 14 and the second core section 28. Asbest seen in FIG. 2B, the second core section 28 is positioneddownstream from the first core section 22 with respect to the flowdirection A of the common fluid through the first and second coresections 22 and 28 to receive the common fluid after it has passedthrough the first core section 22.

While the common fluid, first fluid, and second fluid can be any fluidsthat require the exchange of heat in a system, in one preferredembodiment for automotive or truck-type applications, the common fluidis air and one of the first and second fluids is refrigerant with one ofthe core sections 22,28 being a condenser, and the other of the firstand second fluids is oil, such as transmission oil, and the other coresection 22,28 being an oil cooler.

As best seen in FIG. 3, each of the first and second cores 22 and 28includes a plurality of parallel, spaced, flattened tubes 30 and 32,respectively, with each of the tubes 30 and 32 having one end receivedin one of the header pipes 12,14 and an opposite end received in theother header pipe 12,14 to direct the corresponding one of the first andsecond fluids between the first and second header pipes 12 and 14through an interior of the tube 30,32. Each of the first and secondcores 22 and 28 further includes corrugated or serpentine fins 34 and36, respectively, extending between adjacent pairs of said tubes 30 andthe tubes 32, respectively, to act as surface enhancements for the flowof the common fluid over the exterior of the tubes 30,32 and the fins 34and 36. As also seen in FIG. 3 each of the header pipes 12,14 ispreferably provided in the form of a cylindrical tube that has piercedtube slots or openings 40 to receive the ends of the tubes 30 and 32,with the end being sealingly bonded in the openings 40 using anysuitable technique, such as by brazing. Each of the header pipes 12,14further includes a pair of end baffles 42 and 44 to close the open endsof the headers pipe 12, 14 adjacent the folded portion 20. Preferably,the baffles 42 and 44 are inserted through cut baffle slots 46 and 48,respectively, and bonded in place, preferably during a common brazingoperation that brazes all of the tubes 30 and 32, fins 34 and 36, andheader pipes 12 and 14 together.

As best seen in FIGS. 2A, 2B, and 3, a cut 50 (typically made by a sawor grinder) is preferably created in each of the header pipes 12,14between the first and second manifolds 16 and 18. The cut 50 onlypartially severs the header pipe 12,14, thereby leaving the foldedportion 20, which is a tab 51 of the common material that forms theheader pipe 12,14 which is left after the cut 50 has been formed. Thecut 50 is preferably created after the remainder of the heat exchanger10 has been assembled and brazed together, but may be created at anypoint during manufacture and assembly, including prior to assembly ofall of the components of the heat exchanger 10 and/or prior to thebrazing operation.

While a preferred embodiment of the heat exchanger 10 has been describedabove in some detail, it should be appreciated that there are manysuitable forms for the various components of the heat exchanger 10. Forexample, while flattened tubes 30,32 have been shown, circular tubes ortubes of another cross sectional shape may prove desirable in someapplications. By way of further example, while serpentine fins 34,36have been shown, other fins, such as plate fins may be desirable in someapplications. As yet a further example, while the header pipes 12 and 14have been shown in the form of generally cylindrical tubes, with thebaffles 42 and 44 inserted through baffle slots 46 and 48, other knownheader constructions and/or baffle constructions may be used, such asfor example two piece header pipe designs utilizing a header plate andtank, and/or baffles that are inserted either through open ends of theheader pipes or between header and tank pieces of a header pipe. As onelast example, while each of the heat exchanger cores 22 and 28 have beenshown as single pass cores, it may be desirable to provide multi-passingin one or both of the cores 22 and 28, such as by using baffles in oneor both of the header pipes 12 and 14 to direct the corresponding fluidflow in multiple passes through the tubes, or by using serpentine tubes.

During assembly of the heat exchanger 10, the cores 22 and 28 arepreferably first assembled together in a fixture with the tubes 30 andfins 34 interleaved and the tubes 32 and fins 36 interleaved, and aspacer in the form of a blank bar or tube 52 positioned at the interfacebetween the cores 22 and 28 with no braze or braze coating so that thespacer 52 does not bond or braze to the adjacent fins 34 and 36. Thecores are then compressed between sideplates 54 and 56, as is known, andthe header pipes 12 and 14 are assembled to the cores with the ends ofthe tubes 30,32 received in the openings 40. The spacer 52 allows forthe cores 22 and 28 to be compressed together. The assembled heatexchanger 10 is then brazed using a suitable braze operation. If thecuts 50 have not yet been made in the header pipes 12 and 14, the cuts50 are next made using a suitable machining technique, such as by sawingor by grinding, and the heat exchanger is folded at the location of thecuts 50 so that the cores 22 and 28 are positioned in a seriesrelationship with respect to the flow direction A of the common flowthrough the cores 22,28, with one of the cores 22 and 28 beingpositioned downstream from the other core 22,28 with respect to thecommon flow and connected by the folded portions 20 of the header pipes12 and 14, as seen in FIGS. 1B and 2B. It should be noted that during orbefore folding, the spacer 52 can be removed because it should not havebonded or brazed to the adjacent fins 34 and 36. After the foldingoperation, a structural support 60, such as a clip in bracket 62, seenin FIG. 2B, is preferably attached to one of the header pipes 12 and 14connected to both the first and second manifolds 16 and 18 at a locationspaced from the folded portion 20. If desired, another structuralsupport 60 can be provided on the other header pipes 12,14.

FIG. 4 shows an alternative embodiment of the heat exchanger 10 whereinthe cuts 50 completely severe each of the headers pipes 12 and 14 sothat the cores 22 and 28 are completely separated. The cores 22 and 28are than connected in the series relationship described above using anysuitable structural bracket or frame.

FIGS. 5 and 6 show yet further alternate embodiments of the heatexchanger 10 wherein there is an additional core section 70, additionalfluid manifold 72, and an additional set of cuts 50 and folded portions20, with the embodiment of FIG. 5 having the core section 70 placed inseries relationship with the core section 22, and FIG. 6 showing thecore section 70 being in series relationship with both the core sections22 and 28, with respect to the direction of the common flow A throughthe heat exchanger 10.

It should be appreciated that the heat exchanger 10 enjoys the processcost savings associated with assembling and brazing a combination-type,multi-fluid heat exchanger utilizing common header pipes 12,14, whileaccommodating the available space requirements for a particularapplication by allowing the core sections 22 and 28 to be placed in aseries relationship with respect to the direction of the common flow Athrough the heat exchanger 10.

1. A multi-fluid heat exchanger for transferring heat between a commonfluid and a first fluid in one part of the heat exchanger and betweenthe common fluid and a second fluid in another part of the heatexchanger, the heat exchanger comprising: a pair of spaced, elongatedheader pipes to direct the first and second fluids to and from the heatexchanger, each of the header pipes including a first fluid manifold forthe first fluid and a second fluid manifold for the second fluid withthe first and second fluid manifolds connected by a folded portion ofthe elongate header pipe; a first core section to transfer heat betweenthe common fluid and the first fluid as the common and first fluids passthrough the first core section, the first core section extending betweenthe header pipes and connected at opposite sides to the first fluidmanifold in each header to transfer the first fluid between the headerpipes and the first core section; and a second core section to transferheat between the common fluid and the second fluid as the common andsecond fluids pass through the second core section, the second coresection extending between the header pipes and connected at oppositesides to the second fluid manifold in each header to transfer the secondfluid between the header pipes and the second core section, the secondcore section positioned downstream from the first core section withrespect to a flow direction of the common fluid through the first andsecond core sections to receive the common fluid after it has passedthrough the first core section.
 2. The multi-fluid heat exchanger ofclaim 1 further comprising a structural support on one of said headerpipes and connected to both the first and second fluid manifolds at alocation spaced from said folded portion.
 3. The multi-fluid heatexchanger of claim 1 wherein the first and second manifolds of eachheader pipe are separated from each other by a cut portion locatedadjacent the folded portion.
 4. The multi-fluid heat exchanger of claim1 wherein each of the header pipes comprises a cylindrical tube having aplurality of tube receiving openings spaced along a length of the headerpipe to receive ends of heat exchange tubes from the first and secondcores.
 5. The multi-fluid heat exchanger of claim 4 wherein each of thefirst and second cores comprises a plurality of parallel, spaced,flattened tubes, each of the tubes having a first end and a second end,with the first end received in one of the header pipes and the secondend received in the other header pipe to direct the corresponding one ofthe first and second fluids between the first and second header pipesthrough an interior of the tube.
 6. The multi-fluid heat exchanger ofclaim 5 wherein each of the first and second cores further comprisescorrugated fins extending between adjacent pairs of said tubes.
 7. Themulti-fluid heat exchanger of claim 1 further comprising a third coresection to transfer heat between the common fluid and a third fluid asthe common and third fluids pass through the third core section, thethird core section extending between the header pipes and connected atopposite sides to a third fluid manifold in each header to transfer thethird fluid between the header pipes and the third core section, thethird fluid manifold connected to one of the first and second fluidmanifolds by another folded portion of the elongate header pipe, thethird core section positioned relative to at least one of the first andsecond core sections so that the common fluid passes through the thirdcore section and the at least one of the first and second core sectionsin series fashion.
 8. A multi-fluid heat exchanger for transferring heatbetween a first fluid and a common fluid in one part of the heatexchanger and between a second fluid and the common fluid in a secondpart of the heat exchanger, the heat exchanger comprising: a firstelongated header pipe having a plurality tube receiving openings spacedalong a length of the first header pipe; a second elongate header pipehaving a plurality of tube receiving openings spaced along a length ofthe second header pipe; a first core section comprising a plurality ofparallel, spaced tubes, each of the tubes having a first end and asecond end, with the first end received in a corresponding one of thetube receiving openings of the first header pipe and the second endreceived in a corresponding one of the tube receiving openings of thesecond header pipe to direct the first fluid between the first andsecond header pipes through an interior of the tube; a second coresection comprising a plurality of parallel, spaced tubes, each of thetubes having a first end and a second end, with the first end receivedin a corresponding one of the tube receiving openings of the firstheader pipe and the second end received in a corresponding one of thetube receiving openings of the second header pipe to direct the secondfluid between the first and second header pipes through an interior ofthe tube; and each of the header pipes having a folded portion at alocation between the first and second cores to locate the second coredownstream from the first core with respect to a flow path of the commonfluid through the first and second cores.
 9. The multi-fluid heatexchanger of claim 8 wherein each of the header pipes comprises a cutadjacent the folded portion between the first and second manifolds. 10.The multi-fluid heat exchanger of claim 8 wherein each of the headerpipes comprises a cylindrical tube having the tube receiving holesformed therein.
 11. The multi-fluid heat exchanger of claim 8 furthercomprising a structural support on one of said header pipes andconnected to both the first and second fluid manifolds at a locationspaced from said folded portion.
 12. The multi-fluid heat exchanger ofclaim 8 wherein the tubes of at least one of the cores are flattenedtubes and the at least one of the cores further comprises corrugatedfins extending between each adjacent pair of flattened tubes.
 13. Themulti-fluid heat exchanger of claim 7 further comprising a third coresection to transfer heat between the common fluid and a third fluid asthe common and third fluids pass through the third core section, thethird core section extending between the header pipes and connected atopposite sides to a third fluid manifold in each header to transfer thethird fluid between the header pipes and the third core section, thethird fluid manifold connected to one of the first and second fluidmanifolds by another folded portion of the elongate header pipe, thethird core section positioned relative to at least one of the first andsecond core sections so that the common fluid passes through the thirdcore section and the at least one of the first and second core sections.14. A method of making a multi-fluid heat exchanger for transferringheat between a first fluid and a common fluid in one part of the heatexchanger and between a second fluid and the common fluid in a secondpart of the heat exchanger, the method comprising the steps of: a)providing a heat exchanger with first and second core sections extendingbetween a pair of elongated header pipes, with each of the header pipeshaving a first fluid manifold for the first core section and a secondfluid manifold for the second core section; b) providing a cut portionin each of the header pipes at a location between the first and secondfluid manifolds, the cut portion leaving at least part of the headerpipe connecting the first and second fluid manifolds of the header; andc) folding the heat exchanger at the cut portion so that the at leastpart of the header pipe is deformed and the first and second coreportions are located in series with respect to a flow path for thecommon fluid through the first and second core portions.
 15. The methodof claim 14 further comprising the step of connecting the first andsecond manifolds of at least one of the header pipes to each other at alocation spaced from the cut portion after step c).
 16. The method ofclaim 14 further comprising the step of brazing the first and secondcore sections and the pair of elongated header pipes as an assemblyprior to step c).
 17. The method of claim 14 further comprising the stepof brazing the first and second core sections and the pair of elongatedheader pipes as an assembly prior to step b).
 18. The method of claim 14further comprising the steps of: d) providing the heat exchanger with athird core section extending between the pair of elongate header pipes,with each of the header pipes having a third fluid manifold for thethird core section; e) providing an additional cut portion in each ofthe header pipes at a location between the third fluid manifold and oneof the first and second fluid manifolds, the additional cut portionleaving at least part of the header pipe connecting the third fluidmanifold and the one of the first and second fluid manifolds of theheader; and f) folding the heat exchanger at the additional cut portionso that the at least part of the header pipe connecting the third fluidmanifold and the one of the first and second fluid manifolds is deformedand the third core section is located in series with at least one of thefirst and second core sections with respect to a flow path for thecommon fluid through the third core section and the at least one of thefirst and second core sections.
 19. A method of making a pair of heatexchangers for transferring heat between a first fluid and a commonfluid in one of the heat exchangers and between a second fluid and thecommon fluid in the other of the heat exchangers, the method comprisingthe steps of: a) providing a heat exchanger with first and second coresections extending between a pair of elongated header pipes, with eachof the pipes having a first fluid manifold for the first core sectionand a second fluid manifold for the second core section; and b)completely severing each of the header pipes at a location between thefirst and second fluid manifolds to form the pair of heat exchangers,with one heat exchanger comprising the first fluid manifolds and thefirst core section, and the other heat exchanger comprising the secondfluid manifolds and the second core section.
 20. The method of claim 19further comprising the step of securing the pair of heat exchangers toeach other so that the first and second core portions are located inseries with respect to a flow path for the common fluid through the pairof heat exchangers after step b).